Signatures of interactions in the Andreev spectrum of nanowire Josephson junctions (Part I)*

I will report on microwave spectroscopy measurements performed on InAs nanowire weak links between superconductors. The properties of the weak link, like the Josephson supercurrent, arise from the localized Andreev states that form at the link. In semiconducting nanowires, the spin-orbit coupling leads to a spin-splitting of the Andreev states when a superconducting phase difference is applied across the weak link [1]. In our experiments, we use a circuit-QED setup to probe the spectrum of Andreev states: the weak link shifts the resonance frequency of a coupled microwave resonator [1-3]. The spin-splitting of the Andreev states gives rise to a distinct phase dependence of the transition lines [1]. In addition, the comparison between data and theory shows that an interacting model is needed to account for several spectral line.

[1] 'Spin-Orbit Splitting of Andreev States Revealed by Microwave Spectroscopy', L. Tosi, C. Metzger, M. F. Goffman, C. Urbina, H. Pothier, Sunghun Park, A. Levy Yeyati, J. Nygård, and P. Krogstrup, Phys. Rev. X 9, 011010 (2019)

[2] 'From Adiabatic to Dispersive Readout of Quantum Circuits', Sunghun Park, C. Metzger, L. Tosi, M. F. Goffman, C. Urbina, H. Pothier, and A. Levy Yeyati, Phys. Rev. Lett. 125, 077701 (2020)

[3] 'Circuit-QED with phase-biased Josephson weak links', C. Metzger, Sunghun Park, L. Tosi, C. Janvier, A. A. Reynoso, M. F. Goffman, C. Urbina, A. Levy Yeyati, and H. Pothier, Phys. Rev. Research 3, 013036 (2021)